Jet Set Radio Future is a completely different game to the original.
Crazy Taxi controls poorly on XBox and PS2.
Sonic Adventure 1 on GC is a bad port apparently.
Powerstones may be on PSP but you can't get a bunch of mates round and sit there having a laugh on that version.
Not to mention there are hoardes of great DC games not available on other systems:
Shenmue, Fur Fighters (the PS2 version is very different visually), MDK 2, VF3tb, Soul Calibur (the sequels suck), Vampire Chronicles, Zero Gunner 2, Border Down, Cosmic Smash, Bangi-O (the N64 JAP version was quite different), Outtrigger, Quake 3 Arena (walks all over PS2 version), Carrier, Propellor Arena, Chu Chu Rocket, 4 Wheel Thunder, Rayman 2 (the best version), Spawn, Trickstyle and a lot more!
I'll give you Jet Set Radio. I actually loved the first one, but didn't care for the second. I haven't played Crazy Taxi on PS2, but Crazy Taxi 3 controlled fine on Xbox. I prefer Sonic Adventure 2 to the first, and that is a fine port. Like I said I can't get Powerstone anyway, so I hope that at some point it will come out on another home console (I doubt it will though).
I have never played Shenmue, so I have no fond memories that make me miss it. I never cared much for Fur Fighters because I know of so many better 4-player games. Soul Calibur 2 is actually about the same game as the first, so I can't see how you can possibly think it sucks. I didn't like Quake 3, and I mentioned Chu Chu Rocket. Rayman 2 is on 64; I know you said best version, but I'm sure it is fine on 64.
The rest of the games you listed I've never played, never heard of, or in 2 cases don't know the game you mean. I know MDK is a common abbreviation for something, but I have no idea what VF3tb is. I'm guessing Virtua Fighter (although I have no idea what tb stands for), in which case I don't care because the only 3d fighter I like is Soul Calibur. In any case, I'm not saying the Dreamcast sucks, or there isn't a reason to own one anymore. I just played mine enough that I don't really miss it, or any of the games I had. I might get another some day and pick up the games I never tried.
MDK, is actually the real name of a game. It supposed to stand for "Murder Death Kill" but noone is certain. But the only thing the case to the game says is MDK, but not what it stands for. MDK for PSX is kind of out dated because of its clunky controls (Just like almost every PSX shooter that doesn't use dual analog), but MDK 2 for the Dreamcast is awesome. It looks great even today. It is an arcade style shooter that is hillarious and has a ton of variety. I heard the port to the PS2 is even better than the dreamcast version, and you can find it at any used game store for about 5 bucks. Well worth the price. But MDK and many of the other games Blue Monkey mentioned wouldn't be on a Sega Dreamcast collection, because Sega doesn't own the rights to them.